Ink remaining amount measuring device, ink-jet recorder comprising same, ink remaining amount measuring method, and ink cartridge

ABSTRACT

In order to provide an ink level detecting unit of an ink jet recording apparatus, which detects surely residual vibration by resonance with a medium such as ink coming into contact with a vibration element without receiving influences such as noise, thereby to heighten ink detection accuracy and reliability, there are provided a piezoelectric element  12  provided in an ink tank  11 , an excitation pulse generating part  13  for applying an excitation pulse to the piezoelectric element  12 , a sensor  14  which detects a frequency of a counter electromotive force waveform from the piezoelectric element  12  based on residual vibration by resonance with a medium in the ink tank  11 , and a judgment part  15  which judges the existence of ink on the basis of the detected frequency. The sensor  14  has two band pass filters  22 A and  22 B which cause only waveforms in the predetermined frequency bands that have been previously assumed according to ink presence and ink absence to pass; and a frequency measuring part  150  which binarizes the counter electromotive force waveform, counts the number of pulses of the binarized counter electromotive force waveform, counts time from the predetermined number-th pulse to the predetermined number of pulse, and detects a frequency of the counter electromotive force waveform on the basis of this time.

TECHNICAL FIELD

The present invention relates to an ink level detecting unit of an inkjet recording apparatus and an ink level detecting method, andparticularly to technology in which change of sound impedance isdetected thereby to detect ink level in an ink tank of an ink jetrecording apparatus.

BACKGROUND ART

Generally, an ink jet recording apparatus includes a carriage on whichan ink jet recording head having a pressure generating means thatpressurizes a pressure generating chamber, and a nozzle opening fromwhich the pressurized ink is ejected as an ink droplet is mounted; andan ink tank which houses ink to be supplied through a flowing path tothe recording head. The ink jet recording apparatus is constituted sothat continuous printing can be performed.

Here, the ink tank is constituted generally as a cartridge that isdetachable from the recording apparatus so that a user can easilyexchange it when the ink has been used up.

As methods of managing ink consumption of a conventional ink cartridge,there have been known a method of managing ink consumption oncalculation by adding up the count number of the ink droplets ejected bythe recording head, and the quantity of ink absorbed in a maintenanceprocess of a print head by use of software; and a method of managing inkconsumption by detecting, by attaching two electrodes for directlydetecting a liquid level to the ink cartridge, the time when thepredetermined quantity of ink has been actually consumed.

However, in the method of managing the ink consumption on calculation byadding up the ejection number of the ink droplets and the quantity ofthe absorbed ink by use of software, depending on environments of use,for example, by rise and fall of temperature or humidity in a usingroom, the elapse time since opening of the ink cartridge, and differenceof a using frequency on user's side, pressure in the ink cartridge andviscosity of ink change. Therefore, there is a problem that an errorthat is not negligible is produced between the ink consumed quantity oncalculation and the actual ink consumed quantity. Further, by individualdifference of the ink jet head, the ink quantity per dot varies, therebyto also cause the problem that an error is produced between the inkconsumed quantity on calculation and the actual ink consumed quantity.Further, in case that a cartridge is once detached and the samecartridge is attached again, the added count value is once reset, sothat there is also a problem that the actual ink level is unclear.

On the other hand, in the method of managing the time when the ink hasbeen consumed by the electrodes, the actual quantity in a point of theink consumption can be detected. Therefore, the ink level can be managedwith high reliability. However, in order to detect liquid level of ink,the ink must be conductive, so that the kind of used ink is limited.Further, there is a problem that liquid closeness structure between theelectrode and the ink cartridge is complicated. Further, since theprecious metal that is good in conductivity and also high in corrosionresistance is usually used as a material of the electrode, there is alsoa problem that the manufacturing cost of the ink cartridge increases.Further, since the two electrodes must be attached respectively to thedifferent positions of the ink cartridge, there is also a problem that amanufacturing process is complicated thereby to cause the increase ofthe manufacturing cost.

On the contrary, an ink level detecting unit has been also proposed,which detects existence of the ink on the basis of a residual vibrationfrequency of a vibration element such as a piezoelectric element.Namely, the residual vibration frequency of the vibration element suchas the piezoelectric element, when the vibration element such as thepiezoelectric element and a medium (ink, air or the like) that comesinto contact with this vibration element are in a resonant state, meansa resonant frequency between the vibration element such as thepiezoelectric element and the medium that comes into contact with thisvibration element. In the above ink level detecting unit, the state ofthe ink that is the medium is detected by change of this resonantfrequency.

In widely various electronic apparatuses, from a viewpoint ofenergy-saving, a tendency to set a drive voltage low is spreading. In anink jet printer, also, the need of making the drive voltage low isincreasing.

In the above ink level detecting unit, conventionally, the piezoelectricelement is pulse-driven at the drive voltage of, for example, 5V therebyto find the above residual vibration frequency.

However, with lowering of the drive voltage, in case that the drivevoltage of the above piezoelectric element is set, for example, at 3.3V,the vibration applied to the piezoelectric element becomes small becauseof lowering of the drive voltage. Therefore, the amplitude of the aboveresidual vibration becomes also small, so that the level of thedetection signal by this residual vibration lowers.

Therefore, in case that the existence of the ink in the ink tank isdetected on the basis of the detection signal of this residualvibration, since the level of the detection signal lowers, the ink leveldetecting unit is easy to receive influences such as noise by motors ofthe ink jet recording apparatus or noise by inducement of a head drivewaveform. As described above, the ink level detecting unit which detectsthe existence of the ink on the basis of the residual vibrationfrequency of the vibration element is sensitive to the noise, so thatthere is a problem that detection accuracy lowers under the environmentin which the noise is large, and the detection becomes difficultoccasionally.

Further, in such the ink level detecting unit, when the position of theliquid level of the ink is nearly equal to the position of the vibrationelement such as the piezoelectric element that functions as a sensingelement (when the liquid level is in a boundary region of ink presenceand ink absence), in case that foaming and waving of the liquid level ofthe ink are produced with movement of the carriage, there is fear oferroneous detection on the existence of ink.

Therefore, an object of the invention is to provide ink level detectingtechnology of an ink jet recording apparatus in which excitation isapplied to a vibration element such as a piezoelectric element, andresidual vibration by resonance between the vibration element and amedium such as ink that comes into contact with the vibration element issurely detected without receiving an influence of noise, thereby toincrease ink detecting accuracy and reliability.

Further, another object of the invention is to provide ink leveldetecting technology of an ink jet recording apparatus in whichexcitation is applied to a vibration element such as a piezoelectricelement, and it is possible to prevent residual vibration by resonancebetween the vibration element and a medium such as ink that comes intocontact with the vibration element, also in case that foaming and wavingof a liquid level of ink are produced by movement of a carriage, frombeing detected erroneously.

DISCLOSURE OF THE INVENTION

In order to solve the above problems, in the invention, there isprovided at least one filter means which causes, of counterelectromotive force waveforms from the vibration element, only awaveform in the predetermined frequency band that has been previouslyassumed according to the presence or absence of ink to pass; and thefrequency of the counter electromotive force waveform that has passedthrough this filter means is detected, whereby the existence of ink isjudged surely without the influence of the noise.

Namely, an ink level detecting unit of the invention is an ink leveldetecting unit of an ink tank, which includes a vibration elementprovided for the ink tank, an excitation pulse generating part whichapplies an excitation pulse to this piezoelectric element, a sensorwhich detects a frequency of a counter electromotive force waveform fromthe vibration element based on residual vibration by resonance with amedium in the ink tank, and a judgment part which judges the existenceof ink on the basis of the frequency detected by the sensor. This unitis characterized in that the sensor includes at least one filter meanswhich causes only a waveform in the predetermined frequency band thathas been previously assumed according to the presence or absence of inkto pass, and a frequency detecting means which binarizes the counterelectromotive force waveform from the vibration element, counts thenumber of pulses of the binarized counter electromotive force waveform,counts time from the predetermined number-th pulse to the predeterminednumber of pulse, and detects the frequency of the counter electromotiveforce waveform on the basis of this time.

According to this constitution, by at least one filter means, withoutcausing noise to pass, the frequency of the counter electromotive forcewaveform from the vibration element based on the residual vibration byresonance with the medium in the ink tank can be detected. Therefore,the existence of the ink can be surely judged.

Further, the ink level detecting unit of the invention is characterizedin that: the filter means comprises a band pass filter for ink presence,and a band pass filter for ink absence, which cause only the waveformsin the predetermined frequency bands that have been previously assumedaccording to the presence and absence of ink respectively to pass; andthe frequency detecting means detects the frequency of the counterelectromotive force waveform that has passed through the band passfilter for ink presence or the band pass filter for ink absence.

According to this constitution, it is possible to detect the frequencyof only the counter electromotive force waveform that has passed throughthe band pass filter for ink presence or the band pass filter for inkabsence which causes only the waveform in the predetermined frequencyband that has been previously assumed according to the presence orabsence of ink. Therefore, without the influence of the noise, theexistence of the ink can be surely judged.

Further, the ink level detecting unit of the invention is characterizedin that the frequency detecting means comprises a frequency counter forink presence which detects a frequency of the waveform that has passedthrough the band pass filter for ink presence, and a frequency counterfor ink absence which detects a frequency of the waveform that haspassed through the band pass filter for ink absence.

According to this constitution, at two measurement circuits in which theband pass filter for ink presence and the frequency counter for inkpresence, and the band pass filter for ink absence and the frequencycounter for ink absence are provided in parallel, the frequency of thecounter electromotive force waveform from the vibration element based onthe residual vibration can be detected simultaneously.

Further, the ink level detecting unit of the invention is characterizedin that: in the band pass filter for ink presence and the band passfilter for ink absence, each center frequency is matched with a resonantfrequency of the vibration element in a case of the ink presence or in acase of the ink absence; and each pass band is set to size that canpermit the individual variation in the vibration element.

According to this constitution, while the individual variation in thesensor is permitted, the invention can be applied to an ink jetrecording apparatus.

Further, the ink level detecting unit of the invention is characterizedin that an insensitive band is provided between the pass bands of bothband pass filter for ink presence and band pass filter for ink absence.

According to this constitution, also when a position of a liquid levelof ink is nearly equal to a position of the vibration element (even whena position of a liquid level of ink is in a boundary region between theink presence and the ink absence), it is possible to prevent erroneousdetection of the existence of the ink due to foaming or waving of theliquid level of the ink with movement of a carriage.

Further, an ink cartridge of the invention, which houses ink used inprinting and is mounted on an ink jet recording apparatus, ischaracterized in that: there are provided a vibration element providedfor the ink cartridge, an excitation pulse generating part which appliesan excitation pulse to this piezoelectric element, a sensor whichdetects a frequency of a counter electromotive force waveform from thevibration element based on residual vibration by resonance with a mediumin the ink cartridge, and a judgment part which judges the existence ofink on the basis of the frequency detected by the sensor; and the sensorincludes at least one filter means which causes only a waveform in thepredetermined frequency band that has been previously assumed accordingto the presence or absence of ink to pass, and a frequency detectingmeans which binarizes the counter electromotive force waveform from thevibration element, counts the number of pulses of the binarized counterelectromotive force waveform, counts time from the predeterminednumber-th pulse to the predetermined number of pulse, and detects thefrequency of the counter electromotive force waveform on the basis ofthis time.

According to this constitution, by at least one filter means, withoutcausing noise to pass, the frequency of the counter electromotive forcewaveform from the vibration element based on the residual vibration dueto resonance with the medium in the ink cartridge can be detected.Therefore, the existence of ink can be surely judged.

Further, an ink level detecting method of an ink jet recording apparatusin the invention is a method of detecting ink level in an ink tank usedin the ink jet recording apparatus by applying an excitation pulse to avibration element provided for the ink tank, detecting a frequency of acounter electromotive force waveform from the vibration element based onresidual vibration due to resonance with a medium in the ink tank, andjudging the existence of ink on the basis of the detected frequency.This method is characterized in that: of counter electromotive forcewaveforms from the vibration element, only a waveform in thepredetermined frequency band that has been previously assumed accordingto the presence or absence of ink is caused to pass by a filter means;the waveform that has passed is binarized and the number of pulses ofthe binarized waveform is counted; time from the predetermined number-thpulse to the predetermined number of pulse is counted; and the frequencyof the counter electromotive force waveform is detected on the basis ofthis time.

According to this constitution, by the filter means, without causing thenoise to pass, the frequency of the counter electromotive force waveformfrom the vibration element based on the residual vibration by resonancewith the medium in the ink tank can be detected. Therefore, theexistence of ink can be surely judged.

Further, the ink level detecting method of the ink jet recordingapparatus in the invention is characterized by using both of the aboveink level detecting method and a method of detecting the ink level bycounting the number of dots of ink ejected from a print head in the inkjet recording apparatus.

According to this constitution, ink-end can be detected more exactlythan in case of detection by only the method of detecting the ink levelby counting the number of dots of ink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the constitution of an ink leveldetecting unit according to a first embodiment of the invention.

FIG. 2 is a wiring diagram showing an example of the concreteconstitution of an amplifier of a sensor in the ink level detecting unitof FIG. 1.

FIG. 3 is a flowchart showing the operation of ink level detection inthe ink level detecting unit of FIG. 1.

FIG. 4 is a time chart showing a signal of each part in measurement of afrequency of residual vibration in FIG. 1.

FIG. 5 is a flowchart showing the detailed operation of measurement(steps A3 and A7 in the flowchart shown in FIG. 3) of the residualvibration frequency in the ink level detecting unit of FIG. 1.

FIG. 6 is a block diagram showing the constitution of an ink leveldetecting unit according to a second embodiment of the invention.

FIG. 7 is a flowchart showing the operation of ink level detection inthe ink level detecting unit of FIG. 6.

FIG. 8 is a diagram for explaining an ink level detecting methodaccording to a third embodiment of the invention.

FIG. 9 is a flowchart showing the operation of ink level detection inthe third embodiment of the invention.

FIG. 10 is an exterior perspective view of an ink cartridge according toa fourth embodiment of the invention.

FIG. 11 is a sectional view of a sensor provided for a side part of theink cartridge shown in FIG. 10.

FIG. 12 is a function block diagram of an ink level detecting circuit ofthe ink cartridge according to the fourth embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described below in detail with reference to modesfor carrying out the invention. The following embodiments do not limitthe invention in claims, and all combinations of features described inthe embodiments are not always indispensable for solving means of theinvention.

An ink level detecting unit according to embodiments of the inventionwill be described below with reference to drawings.

FIG. 1 shows the constitution of an ink level detecting unit accordingto a first embodiment of the invention. In FIG. 1, an ink leveldetecting unit 10 comprises a piezoelectric element 12 functioning as avibration element provided for a cartridge type ink tank 11 attached toan ink jet recording apparatus (ink jet type printer) detachably; anexcitation pulse generating part 13 for applying an excitation pulse tothis piezoelectric element 12; a sensor 14 which detects a frequency ofa counter electromotive force waveform based on residual vibration byresonance with ink produced in this piezoelectric element 12; a judgmentpart 15 which judges the existence of ink; and a control part 200 whichcontrols theses excitation pulse generating part 13, sensor 14, andjudgment part 15.

Here, the piezoelectric element 12 in FIG. 1 is actually, in a printhead unit of an ink jet type printer, provided for an ink tank 11 ofeach color.

The above piezoelectric element 12 is so constituted as to producedisplacement by the applied voltage, resonate to a medium, that is, inkor air in the ink tank 11, and produce residual vibration by thisresonance. By this residual vibration, a counter electromotive forcewaveform is produced in the piezoelectric element 12.

The excitation pulse generating part 13, which registers two kinds ofexcitation pulses previously, is constituted so as to output theseexcitation pulses selectively.

Here, of the two kinds of excitation pulses, a first kind of excitationpulse is an excitation pulse having a pulse width and a pulse periodcorresponding to the residual vibration by the resonance with the inkwhen the ink exists in the ink tank 11. A second kind of excitationpulse is an excitation pulse having a pulse width and a pulse periodcorresponding to the residual vibration by the resonance with the airwhen the ink does not exist in the ink tank 11.

The above sensor 14 shown in FIG. 1 comprises an amplifier 16, a bandpass filter (BPF) for ink presence 22A, a band pass filter (BPF) for inkabsence 22B, and a frequency measuring part 150. The frequency measuringpart 150 further includes a pulse number counter 170 and a pulse widthmeasuring part 180.

The above amplifier 16 is, as shown in FIG. 2, for example, soconstituted that the counter electromotive force waveform from thepiezoelectric element 12 is amplified by an operational amplifier 16 athereby to be made into a waveform having reference voltage Vref in thecenter of vibration.

The above band pass filter (BPF) for ink presence 22A, and the band passfilter (BPF) for ink absence 22B are band pass filters of which therespective center frequencies are matched with frequencies of the outputwaveforms obtained by the ink level detecting unit in the embodiment incase that the ink is present and absent. Namely, in the band pass filter(BPF) for ink presence 22A, its center frequency is matched with 100 kHzfrequency of the output waveform in case the ink is present. On theother hand, in the band pass filter (BPF) for ink absence 22B, itscenter frequency is matched with 160 kHz frequency of the outputwaveform in case the ink is absent.

The above band pass filter (BPF) for ink presence 22A, and the band passfilter (BPF) for ink absence 22B have respectively ±10 kHz pass bandwidth of each center frequency. This takes individual variation in thepiezoelectric element as the sensor into consideration. Namely, the bandpass filter (BPF) for ink presence 22A has 90 kHz to 110 kHz pass bandwidth. On the other hand, the band pass filter (BPF) for ink absence 22Bhas 150 kHz to 170 kHz pass band width. Therefore, 110 kHz to 150 kHzthat is an intermediate frequency region of the pass band widths of theboth filters is set so as to become an insensitive band of the sensor ina way.

A first feature of the embodiment, as described above, is that the twoband pass filters of which respective center frequencies are matchedwith the frequencies of the output waveforms in case the ink is presentand in case that the ink is absent are used.

Further, a second feature of the embodiment is that the pass band widthsof the both filters are set so that the individual variation in thesensor is taken into consideration, and the intermediate frequencyregion between the pass band widths of the both filters becomes theabove insensitive band.

The above frequency measuring part 150 is a single frequency counterprovided for the two filters of the band pass filter (BPF) for inkpresence 22A and the band pass filter (BPF) for ink absence 22B, andconnection of the frequency measuring part 150 is switched, according toa control signal from the control part 200, to either the band passfilter (BPF) for ink presence 22A or the band pass filter (BPF) for inkabsence 22B.

The pulse number counter 170 in this frequency measuring part 150compares the counter electromotive force waveform input from theamplifier 16 through the band pass filter (BPF) for ink presence 22A orthe band pass filter (BPF) for ink absence 22B with the referencevoltage Vref by use of a comparator. In case that the counterelectromotive force waveform is higher than the reference voltage Vref,the pulse number counter 170 outputs a signal thereby to binarize thecounter electromotive force waveform, counts the number of pulses ofthis binarized counter electromotive force waveform, and generates atime count pulse which becomes an H-level only for time from thepredetermined number-th pulse to the predetermined number of pulse (forexample, time from the fifth pulse to the eighth pulse). Further, thepulse width measuring part 180 measures the pulse width of the timecount pulse from the pulse number counter 170, calculates the pulsenumber per unit time, and detects the frequency of the pulse of thecounter electromotive force waveform.

The above judgment part 15, on the basis of the frequency of the pulseof the counter electromotive force waveform detected in the sensor 14,judges the existence of ink in a height position where the piezoelectricelement 12 in the ink tank 11 is provided, and outputs a judgment resultto the control part 200 provided for, for example, a printer body of theink jet type printer.

The above control part 200 comprises, for example, a microcomputer, aCPU, and the like; and controls, in accordance with an ink leveldetecting method of the invention, the excitation pulse generating part13, the sensor 14, and the judgment part 15 thereby to detect the inklevel as described later.

Further, a main control part of the printer body may be constituted soas to have the function of the control part 200.

The ink level detecting unit 10 according to the first embodiment of theinvention is thus constructed, and operates, on the basis of an inklevel detecting method according to the first embodiment of theinvention, in accordance with a flowchart of FIG. 3, as follows.

Firstly, in a step A1, the control part 200 clears a remeasurement flag,and thereafter, sends a control signal in a step A2 thereby to switchthe connection of the frequency measuring part 150 to the band passfilter (BPF) for ink presence 22A. In a step A3, by the excitation pulsegenerating part 13, as a target frequency, that is, an excitation pulse,the excitation pulse when the ink exists is selected, and thisexcitation pulse is generated. Hereby, the excitation pulse shown inFIG. 4A is applied to the piezoelectric element 12, so that thepiezoelectric element vibrates. The ink in the ink tank 11 resonates bythe vibration of the piezoelectric element 12. In result, thepiezoelectric element 12 generates residual vibration by this resonance.Next, the control part 200 controls the sensor 14, and measures thefrequency of the residual vibration of the piezoelectric element 12 asfollows.

Namely, the piezoelectric element 12, by the residual vibration by theresonance with the ink in the ink tank 11, generates a counterelectromotive force waveform as shown in FIG. 4B.

This counter electromotive force waveform is amplified, as shown in FIG.4C, by the operational amplifier 16 a of the amplifier 16 with thereference voltage Vref in the center of vibration. In case that an inkliquid level is higher than a sensor position of the ink tank 11, thatis, a position in which the piezoelectric element 12 is located (in casethat the ink exists), this counter electromotive force waveform has afrequency between 90 KHz to 100 KHz due to the individual variation inthe sensor. Therefore, since its frequency is in the pass bandwidth ofthe band pass filter (BPF) for ink presence 22A, the counterelectromotive force waveform passes through the band pass filter (BPF)for ink presence 22A and is input in the pulse number counter 170 of thefrequency measuring part 150. Then, the pulse number counter 170compares this counter electromotive force waveform with the referencevoltage Vref by use of the comparator, binarizes the counterelectromotive force waveform, as shown in FIG. 4D, counts this binarysignal, and generates, as shown in FIG. 4E, a time count pulse whichbecomes an H-level only for time from the predetermined number-th pulseto the predetermined number of pulse (in FIG. 4E, from the fifth pulseto the eighth pulse).

Hereby, the pulse width measuring part 180 measures the pulse width ofthis time count pulse, and finds a residual vibration frequency fromthis pulse width. At this time, even if high frequency noise due to themotor of the ink jet type printer or due to induction of the head drivewaveform is applied to the sensor system from the piezoelectric element12, the frequency of such the high frequency noise does not exist in thepass band width of the band pass filter (BPF) for ink presence 22A.Therefore, the high frequency noise cannot pass through the band passfilter (BPF) for ink presence 22A, so that it is not input in the pulsenumber counter 170 of the frequency measuring part 150.

Subsequently, in a step A4, the control part 200, by confirming thegeneration of the above time count pulse within the predetermined time,judges whether the frequency measurement of the residual vibration ofthe piezoelectric element 12 by the resonance with the ink hassucceeded. In case that the measurement has succeeded, the control part200 outputs its frequency in a step A5, the judgment part 15 judges theexistence of ink, and the ink level detecting operation ends.

Here, the judgment part 15, by judging the residual vibration frequencyis in the frequency range in case of the ink presence, judges theexistence of the ink.

In case that the residual vibration frequency is not in the frequencyrange in case of the ink presence, processing similar to a case ofmeasurement failure in the step A4 may be performed.

On the contrary, in case that the frequency measurement of the residualvibration has failed in the step A4, the control part 200 sends acontrol signal in a step A6 and switches the connection of the frequencymeasuring part 150 to the band pass filter (BPF) for ink absence 22B.Then, in a step A7, the second excitation pulse when the ink is absentis selected as a target frequency, that is, an excitation pulse of thepiezoelectric element 12, and this second excitation pulse is generated,whereby the piezoelectric element 12 vibrates and resonates with the inkor air in the ink tank 11. The piezoelectric element 12 generatesresidual vibration by resonance with the ink or air. Then, the controlpart 200 controls the sensor 14 as described later, thereby to measurethe frequency of the residual vibration of the piezoelectric element 12.

Subsequently, in a step A8, the control part 200 judges whether thefrequency measurement of the residual vibration has succeeded. In casethat the measurement has succeeded, the control part 200 outputs itsfrequency in the step A5, the judgment part 15 judges the absence ofink, and the ink level detecting operation ends.

In case that the residual vibration frequency is not in the frequencyrange in case of the ink absence, processing similar to a case ofmeasurement failure in the step A8 may be performed.

Further, in case that a remeasurement flag is not set up in a step A9,the control part 200, after setting up the remeasurement flag in a stepA10, waits till a carriage motor for moving the printer head of the inkjet type printer and a paper feeding motor stop and further ink ejectionstops, and returns to the step A2. Hereby, influences such as noise dueto the carriage motor and the paper feeding motor, and noise due todrive waveform signals in the ink ejection are removed, and the inklevel is detected again.

On the contrary, in case that the remeasurement flag is set up in thestep A9, since the remeasurement of the ink level has been performed inthe steps A2 to A8 through the steps A10 to A11, the control part 200performs, as failure of the ink level detection, such appropriateprocessing as to stop the printing operation of the ink jet type printerin a step A12, and the ink level detecting operation ends.

In the above embodiment, the excitation pulse generating part 13registers previously two kinds of excitation pulses corresponding to theresidual vibrations of the piezoelectric element 12 in case of the inkpresence and in case of the ink absence. Firstly, by the firstexcitation pulse in case of the ink presence, the frequency of theresidual vibration is measured. When the measurement fails, thefrequency of the residual vibration is measured by the second excitationpulse in case of the ink absence.

In this case, the residual vibration frequency is measured (the steps A3and A7 in FIG. 3) by the ink level detecting unit 10 in accordance witha flowchart shown in FIG. 5 as follows.

Namely, in case that the target frequency is set to a frequency in caseof the ink presence in the step A2 of the flowchart of FIG. 3, firstly,in a step B1 of the flowchart of FIG. 5, the control part 200 sets thepulse number (Pn) of the first excitation pulse as the target pulse toone (Pn=1) by use of the excitation pulse generating part 13. In a stepB2, the excitation pulse generating part 13 generates one firstexcitation pulse (pulse according to the case of the ink presence), andapplies this excitation pulse to the piezoelectric element 12.

Then, in a step B3, the control part 200 controls the sensor 14 toamplify, by use of the operational amplifier 16 a of the amplifier 16,the counter electromotive force waveform based on the residual vibrationby the resonance with the ink produced in the piezoelectric element 12,compare, in a step B4, the amplified counter electromotive force pulsewith the reference voltage Vref by use of the comparator 16 b, andbinarize this pulse.

Sequentially, the control part 200, in a step B5, causes the pulsecounting part 170 to count the above binary signal and generate a timecount pulse which becomes H-level only for time from the predeterminednumber-th pulse to the predetermined number of pulse (for example, fromthe fifth pulse to the eighth pulse), and causes the pulse widthmeasuring part 180 to measure a pulse width of the above time countingpulse and measure the frequency of the residual vibration of thepiezoelectric element 12.

Next, the control part 200, in a step B6, judges whether the pulse widthhas been able to be measured within the predetermined time or not, thatis, whether the time count is in timeout. In case that the measurementis in timeout (In case of Yes in the step B6), the control part 200, ina step B7, judges whether n has reached a maximum value. In case that ndoes not reach the maximum value, the control part 200, in a step B8,increases the number of pulses by one (n=n+1) thereby to provide twopulses, returns to the step B2, and performs remeasurement. Thisprocessing is repeated, and in case that the vibration frequency cannotbe measured (Yes in the step B7) even if that the number of pulses isincreased till n reaches the maximum value (Pn=Pnmax) in the step B7, itis judged in a step B9 that the ink level detection (measurement) fails,and the control part 200 proceeds to the steps A4 to A6 in the flowchartof FIG. 3. Namely, as the target pulse, the second excitation pulse(pulse according to the case of the ink absence) is set.

On the contrary, in case that the time count is not in timeout in thestep B6, the control part 200 judges in a step 10, whether the frequencyof the residual vibration is in the frequency range in case of the inkpresence. In case that the frequency of the residual vibration is in thefrequency range in case of the ink presence, the control part 200 judgesin a step B11 that the ink is present. In result, the ink leveldetection (measurement)becomes successful, and the control part 200proceeds from the step A4 to the step A5 in the flowchart of FIG. 3.

Further, in the step B10, in case that the frequency of the residualvibration is not in the frequency range in case of the ink presence, thecontrol part 200 judges in a step B12 whether the frequency of theresidual vibration is in the frequency range in case of the ink absence.In case that the frequency of the residual vibration is in the frequencyrange in case of the ink absence, the control part 200 judges in a stepB13 that the ink is absent. Similarly, the ink level detection(measurement) becomes successful, and the control part 200 proceeds fromthe step A4 to the step A5 in the flowchart of FIG. 3.

On the contrary, in the step B12, in case that the frequency of theresidual vibration is not in the frequency range in case of the inkabsence, the existence of ink cannot be judged. Therefore, the controlpart proceeds to the step B7, and performs the processing similar to theprocessing in case of the timeout. Namely, while the number of pulses isincreased to Pnmax, the measurement is repeated. Further, the operationin the step A7 of FIG. 3 (the operation in case that the control partproceeds from the step A7 to the step A8) is also performed inaccordance with the flowchart of FIG. 5 similarly.

Thus, by measuring the residual vibration frequency of the piezoelectricelement 12 by the resonance with the ink in the ink tank 11, thejudgment of the existence of ink can be more exactly performed.

In the conventional ink level detecting unit which utilizes the residualvibration frequency of the vibration element similarly to the unit inthis embodiment, as described before, when the position of the liquidlevel of the ink is nearly equal to the position of the vibrationelement such as the piezoelectric element functioning as a sensingelement (in a boundary region between the ink presence and the inkabsence), in case that foaming and waving of the liquid level of the inkare produced with the movement of the carriage, there is fear oferroneous detection on the existence of ink.

However, in the ink level detecting unit of this embodiment, thefrequency region 110 kHz to 150 kHz between the pass band width of theband pass filter (BPF) for ink presence 22A and the pass band width ofthe band pass filter (BPF) for ink absence 22B is set so as to become aninsensitive band of the sensor in a way. Therefore, when the position ofthe liquid level of the ink in the ink tank 11 is nearly equal to theposition of the vibration element 12 (in the boundary region between theink presence and the ink absence), unevenness of outputs due to foamingand waving of the ink liquid level produced with the movement of thecarriage is shut off by this insensitive band. In result, the aboveerroneous detection is never performed. Namely, in this case, in eitherof the residual vibration frequency measurements in the steps A3 and A7in the flowchart of FIG. 3, the measurements fail, so that the controlpart proceeds to the step 11, waits till the carriage motor for movingthe printer head of the ink jet type printer and the paper feeding motorstop and further ink ejection stops, and returns to the step A2. Hereby,the influences such as noise due to the carriage motor and the paperfeeding motor, and noise due to the drive waveform signals in the inkejection are completely removed, and the ink level is detected again.

As described above, in the ink level detecting unit of the embodiment,even in case that foaming and waving of the ink liquid level areproduced with the movement of the carriage, the erroneous detection canbe prevented.

Further, in either of the residual vibration frequency measurements inthe steps A3 and A7 in the flowchart of FIG. 3, as described above, evenif the high-frequency noise due to the motor of the ink jet type printeror due to induction of the head drive waveform is applied to the sensorsystem from the piezoelectric element 12, the frequency of such the highfrequency noise does not exist in the pass band widths of the band passfilter (BPF) for ink presence 22A and the band pass filter (BPF) for inkabsence 22B. Therefore, the high frequency noise cannot pass through theband pass filter (BPF) for ink presence 22A or the band pass filter(BPF) for ink absence 22B, so that it is not input in the pulse numbercounter 170 of the frequency measuring part 150. Accordingly, the exactdetection of the existence of ink in which the influence of such thenoise is eliminated can be performed.

In the ink level detecting unit of the embodiment, since the influencesof the noises due to the motors such as the carriage motor and due tothe drive waveform signal for ink ejection can be eliminated, withoutstopping the printing operation of the ink jet type printer, that is,without stopping the carriage motor and the paper feeding motor, andfurther without stopping the ink ejection by the drive waveform signal,the comparatively exact detection of the existence of ink can beperformed. Therefore, though the detection can be performed also duringmovement (main scan) of the carriage, it is preferable, as timing ofdetection, to perform the detection, of a series of moving operations ofthe carriage which comprise the steps of accelerating from a stopposition, printing at a constant speed, decelerating, and stopping,during printing at the constant speed. This is because foaming andwaving of the liquid level of the ink with the movement of the carriageare comparatively little.

FIG. 6 shows the constitution of an ink level detecting unit accordingto a second embodiment of the invention. The basic constitution of theink level detecting unit of this embodiment is nearly the same as thatin the first embodiment. The similar parts to those in the firstembodiment are denoted with the similar reference numerals, and theirdescription is omitted. In FIG. 6, a sensor 14′ comprises an amplifier16, a band pass filter (BPF) for ink presence 22A, a frequency measuringpart 150A connected to the band pass filter (BPF) for ink presence 22A,a band pass filter (BPF) for ink absence 22B, and a frequency measuringpart 150B connected to the band pass filter (BPF) for ink absence 22B.The frequency measuring part 150A further includes a pulse numbercounter 170A and a pulse width measuring part 180A, and the frequencymeasuring part 150B further includes a pulse number counter 170B and apulse width measuring part 180B. As described above, this embodiment ischaracterized in that: there are two frequency measuring circuits whichcomprise the band pass filter (BPF) for ink presence 22A and thefrequency measuring part 150A connected to the band pass filter (BPF)for ink presence 22A, the band pass filter (BPF) for ink absence 22B andthe frequency measuring part 150B connected to the band pass filter(BPF) for ink absence 22B; and a frequency of a pulse in case of inkpresence and a frequency of a pulse in case of ink absence are measuredin their respective circuits.

The ink level detecting unit 10′ according to the second embodiment ofthe invention is thus constructed, and operates, on the basis of an inklevel detecting method according to the second embodiment of theinvention, in accordance with a flowchart of FIG. 7, as follows.

Firstly, in a step C1, a control part 200 clears a remeasurement flag,and thereafter, a frequency of residual vibration of a piezoelectricelement 12 is measured simultaneously in the BPF circuit for inkpresence comprising the band pass filter (BPF) for ink presence 22A andthe frequency measuring part 150A and the BPF circuit for ink absencecomprising the band pass filter (BPF) for ink absence 22B and thefrequency measuring part 150B. Namely, in a step C2A, by an excitationpulse generating part 13, as a target frequency, that is, an excitationpulse, an excitation pulse when the ink is present is selected, and thisexcitation pulse is generated. Hereby, the frequency of the residualvibration of the piezoelectric element 12 is measured as shown in FIGS.4A to 4E. Further, in a step C2B, by the excitation pulse generatingpart 13, as a target frequency, that is, an excitation pulse, anexcitation pulse when the ink is absent is selected, and this excitationpulse is generated. Hereby, the frequency of the residual vibration ofthe piezoelectric element 12 is measured as shown in FIGS. 4A to 4E.

At this time, even if high frequency noise due to the motor of the inkjet type printer or due to induction of the head drive waveform isapplied to a sensor system from the piezoelectric element 12, thefrequency of such the high frequency noise does not exist in a pass bandwidth of the band pass filter (BPF) for ink presence 22A, and in a passband width of the band pass filter (BPF) for ink absence 22B. Therefore,the high frequency noise cannot pass through the band pass filter (BPF)for ink presence 22A or the band pass filter (BPF) for ink absence 22B,so that such the noise does not influence the frequency measurement ofthe residual vibration.

Subsequently, in a step C3, the control part 200, by confirming thegeneration of the above time count pulse within the predetermined time,judges whether the frequency measurement of the residual vibration ofthe piezoelectric element 12 has succeeded in the BPF circuit for inkpresence. In case that the measurement has succeeded, the control part200 outputs its frequency in a step C4, the judgment part 15 judges theexistence of ink, and the ink level detecting operation ends. Here, thejudgment part 15, by judging whether the residual vibration frequency isin the frequency range in case of the ink presence, judges the existenceof the ink.

On the contrary, in case that the frequency measurement of the residualvibration has failed in the step C3, the control part 200, in a step C5,by similarly confirming the generation of the above time count pulsewithin the predetermined time, judges whether the frequency measurementof the residual vibration of the piezoelectric element 12 has succeededin the BPF circuit for ink absence. In case that the measurement hassucceeded the control part 200 outputs its frequency in the step C4, thejudgment part 15 judges the absence of ink, and the ink level detectingoperation ends. Here, the judgment part 15, by judging whether theresidual vibration frequency is in the frequency range in case of theink absence, judges the absence of the ink.

On the contrary, in case that the frequency measurement of the residualvibration has failed in the step C5, whether a remeasurement flag is setup or not is judged in a step C6. In case that the remeasurement flag isnot set up, the control part 200, after setting up the remeasurementflag in a step C7, waits till a carriage motor for moving a printer headof an ink jet printer and a paper feeding motor stop and further inkejection stops, and returns to the steps C2A and C2B. Hereby, theinfluences such as noise due to the carriage motor and the paper feedingmotor and noise due to the drive waveform signal in the ink ejection areremoved, and the ink level is detected again.

On the contrary, in case that the remeasurement flag is set up in thestep C6, since the remeasurement of the ink level has been performed inthe steps C2A and C2B to C5 through the steps C7 to C8, the control part200 performs, as failure of the ink level detection, such appropriateprocessing as to stop the printing operation of the ink jet type printerin a step C9, and the ink level detecting operation ends.

The ink level detecting unit 10′ of the embodiment, by the aboveoperations, can obtain the working advantages similar to those in thefirst embodiment.

FIG. 8 is a block diagram showing the whole constitution of a printer300 according to a third embodiment of the invention. The shown printer300 comprises a printer controller 310 and a print engine 320. Theprinter controller 310 includes an interface (hereinafter referred to asa ┌host I/F┘) 311 which receives print data from a host computer 400; aninput buffer 312A for temporarily storing the print data input in theprinter 300; an output (image) buffer 312B in which the print datastored in the input buffer 312A is interpreted and decompressed intoprint image data; a ROM 313 which stores routines for various dataprocessing; a CPU 314; a print control ASIC 315 consisting of a printcontrol circuit for sending head data to a printer head 322, and anapplied semiconductor integrated circuit (hereinafter referred to as a┌ASIC┘) including various motor drivers; and an interface (hereinafterreferred to as a ┌mech. I/F┘) 316 for sending image data and a drivesignal to the print engine 320. The host I/F 311, the input buffer 312A,the output (image) buffer 312B, the ROM 313, the CPU 314, the printcontrol ASIC 315, and the mech. I/F 316 are connected to one another bya bus 317.

The host I/F 311 includes a FIFO buffer which temporarily stores data inorder to transmit and receive the data between the host computer 400 andit, and receives a print command to print data from the host computer400. The input buffer 312A stores temporarily the print data which theFIFO buffer in the host I/F 311 has received. In the output (image)buffer 312B, image data after the print command to the print data havebeen analyzed, for example, raster graphics type image data isdecompressed. The ROM 313 stores various control programs to be executedby the CPU 314. Further, the ROM 313 stores also font data, graphicfunction, and various procedures, which are not shown. The CPU 314 playsa central role of various controls in the printer according to thisembodiment.

The print engine 320 comprises a print head 322, a carriage mechanism324, and a paper feeding mechanism 326. The paper feeding mechanism 326comprises a paper feed motor, a paper feed roller and the like, andfeeds out print recording media such as recording paper successivelythereby to perform sub-scan. The carriage mechanism 324 comprises acarriage on which the print head 322 is mounted, a carriage motor whichruns the carriage through a timing belt, and the like, and moves theprint head 322 in the main scanning direction. An ink cartridgeconstituting an ink tank 11′ in the embodiment is fitted into a housingof the carriage to be set. The print head 322 has, in the sub-scanningdirection, ink jet nozzle arrays, of which one comprises, for example,96 nozzles for each color, and ejects an ink droplet from each nozzle atthe predetermined timing.

The graphics data taken into the host computer 400 through a not-shownimage scanner is converted, by a printer driver on the host computer400, into data (control command and print data) that the printer 300 caninterpret. This converted data, while being managed by an operatingsystem (OS) on the host computer 400, is sent from an interface part(I/F part) of the host computer 400 through a connection cable 415 tothe printer 300.

In the printer 300, firstly, the data is received by the host I/F 311 ofthe printer, its control command and print data are interpreted by theCPU 314 and decompressed into print image data by the output (image)buffer 312B, and printing is executed by the print engine 320. Further,printer status including the ink level is controlled by a not-shownstatus confirmer on the printer 300 side in real time, and transmittedthrough a not-shown data transmission part in the host I/F 311 to thehost computer 400. Then, by the printer driver on the host computer 400,the ink level is displayed on, for example, a not-shown monitor screen.

The embodiment is characterized in that the ink level detecting methodby the above ink level detecting unit (ink level sensor) 10 or 10′according to the first or second embodiment is used together with an inklevel calculating method (software count) by software. Further, asoftware program according to this ink level calculating method iscomposed of the control program which is executed by the CPU 314 andsaved in the ROM 313.

In the embodiment, as the ink level calculating method by software, amethod of calculating the ink level is used, which comprises the stepsof counting the number of ink dots ejected from the printer (print) head322, multiplying the counted number by the ink quantity per dot therebyto find the consumed ink quantity, subtracting this consumed inkquantity from ink total quantity in a virgin state, and furthersubtracting the ink quantity used for maintenance in head cleaning suchas ink suction (pumping).

An ink level calculating expression by this software count isrepresented by the following expression (1):I (remain)=I (full)−(Count×dI)−I(maintain)  (1).

Herein,

I (remain): Residual quantity of ink

I (full): Ink quantity of virgin ink cartridge

Count: Dot count number

dI: Ink quantity per dot

I (maintain) : Ink quantity used for maintenance such as head cleaning

Here, though dI has variations according to individual difference of ahead and the ink status, assumable maximum dI is used for calculation inorder to prevent dry ejection due to ink shortage.

Therefore, in this ink level calculating method by software, withconsumption of ink, errors are gradually stored between the ink level oncalculation and the actual ink level. Therefore, it is supposed that astate where ink is consumed only from a bottom of the ink tank (inkcartridge) 11′ to a height position 81 (ink liquid level) as shown inFIG. 8 is taken as ink-end on the above dot count. Saying in otherwords, the portion (shown by an arrow 82) from the bottom of the inktank 11′ to the ink liquid level position 81, shown in FIG. 8,corresponds to calculation error included in one ink cartridge in theink level calculating method by software, and must be permitted as amargin for preventing the dry ejection due to the ink shortage.

Therefore, in the embodiment, the above ink level detecting methodaccording to the first or second embodiment is used together with theabove ink level calculating method by software, whereby ink can be usedup to the end, that is, the exact detection of ink-end can be performed.

Namely, in the embodiment, the piezoelectric element 12 as a sensingelement in the above ink level detecting unit (ink level sensor) 10 or10′ according to the first or second embodiment is, as shown in FIG. 8,provided on a side surface of the ink tank 11′ and in a higher positionthan the ink liquid level position 81 that is a boundary by the softwarecount. In order to perform more exact ink-end detection, it ispreferable that the piezoelectric element 12 is provided in a positionthat is higher than the ink liquid level position 81 and close to thebottom of the ink tank 11′. In case that the full quantity of ink is inthe ink tank (ink cartridge) 11′, the ink state is judged to be inkpresence by the ink level detecting unit (ink level sensor) 10 or 10′including the piezoelectric element 12. Therefore, the detection of theink level is continued by the ink level detecting unit (ink levelsensor) 10 or 10′. In the boundary region (shown by an arrow 83) betweenthe ink presence and the ink absence (When the ink absence is firstlyjudged), since the residual ink quantity from the position where thepiezoelectric element 12 is fixed is exactly known, the calculationerror stored in the ink level calculation by the software is removed atthis time, the dot count is anew performed from this position, and theink is consumed to the ink-end. Though, also in the region shown by thearrow 83 in FIG. 8, the errors are included in the ink level calculationby the software, the stored errors are corrected in the region till theink level detecting unit (ink level sensor) 10 or 10′ detects the inkabsence. Therefore, the ink can be used to an ink liquid level position84, so that the quantity of ink that remains in the ink cartridge (inktank 11′) in the ink-end can be reduced.

As shown in FIG. 8, the piezoelectric element 12 is provided in thehigher position than the ink liquid level position 81 that is the limitof the software count. Therefore, though the ink level detecting unit(ink level sensor) 10 or 10′ judges that the ink is present, in casethat the ink-end is detected by the ink level calculation by thesoftware, it is thought that any troubles are produced in the ink leveldetecting unit (ink level sensor). Therefore, in order to prevent dryejection due to the ink shortage, that time is judged to be the ink-end.

An ink level detecting method in the embodiment will be described belowwith reference to a flowchart of FIG. 9.

Firstly, in a step D1, use of the ink cartridge (ink tank 11′) isstarted; and in a step D2, as the printing operation is executed, theink is consumed more, and the ink in the ink cartridge (ink tank 11′)decreases more. In a step D3, the ink level is calculated by the abovesoftware count. In a step D4, the ink level detecting unit (ink levelsensor) 10 or 10′ performs the ink level detection at the predeterminedtiming. Whether the ink level detecting unit (ink level sensor) 10 or10′ has detected the ink absence or not is judged (step D5). In casethat the ink absence has been detected (Yes in the step D5), theabove-mentioned ink level calculation expression by the software countis corrected (step D6).

Namely, in case that the ink quantity (shown by the arrow 83) from theposition of the piezoelectric element 12 of the ink level detecting unit(ink level sensor) 10 or 10′ to the bottom of the ink tank 11′ is takenas I (few), when the sensor detects the ink absence, the accumulativecalculation errors can be made zero by the following setting:

I (remain)=I (few)

I (full)=I (few)

Count=0

I (maintain)=0

Further, the ink level calculation by the software count is anewperformed after this setting to perform printing, whereby the quantityof ink that remains in the ink cartridge when the ink is judged to bethe ink-end can be reduced.

Further, when the ink level detecting unit (ink level sensor) 10 or 10′detects the ink absence, the above dI can be corrected from thedifference between the ink level on calculation and the actual inklevel. Using this corrected dI, the ink quantity that remains in theportion lower than the piezoelectric element 12 of the ink leveldetecting unit (ink level sensor) 10 or 10′ is calculated, whereby moreexact judgment of ink-end can be performed, and the ink residualquantity can be more reduced. In case that the ink quantity per dot isdifferent between printing modes, dots should be counted in eachejection mode, and using ratio of the ink quantity in each mode, the inklevel calculation and the correction of the calculation expressionshould be performed.

After the ink level calculation expression has been thus corrected (stepD6), the printing operation is continued in a step D7. Hereby, the inkis further consumed, and the ink in the ink cartridge (ink tank 11′)further decreases. In a step D8, the ink level is calculated by theabove software count. Then, whether the ink level by the software counthas come to zero or not is judged (step D9). In case that the ink levelhas come to zero (Yes in the step D9), this state is judged to beink-end (step D10). Then, as described above, the ink-end is displayedon a not-shown monitor screen by a printer driver on the host computer400 shown in FIG. 8 to inform the user of the ink-end (step D11), andthe ink level detecting operation ends.

On the other hand, in case that the ink absence has not been detected inthe step D5 (No in the step D5), whether the ink level by the softwarecount is zero or not is judged (step D12). In case that the ink level iszero (Yes in the step D12), the ink cartridge (ink tank 11′) is judgedto be abnormal (step D13). Then, abnormality of the ink cartridge isdisplayed on the monitor screen to inform the user of the abnormality(step D14), and the ink level detecting operation ends. On the otherhand, in case that the ink level by the software count is not zero (Noin the step D12), the ink level detecting operation returns to the stepD2, and the printing operation is continued.

As described above, according to the ink level detecting method in theembodiment, the above-described ink level detecting method according tothe first or second embodiment is used together with the ink levelcalculating method by software, whereby the ink can be used up to theend, that is, the more exact detection of ink-end can be performed.

In the above embodiments, though, as the vibration element, thepiezoelectric element is used, the invention is not limited to this butother piezoelectric elements such as an electrostrictive element and amagentrostrictive element, or other vibration elements may be used.

Further, though, in the above embodiments, the single ink tank 11 isshown, the invention is not limited. It is clear that an ink jet printerwhich performs color printing of four to seven colors may detect the inklevel by providing a vibration element for each ink tank of each color,and detecting a frequency of a counter electromotive force waveformbased on residual vibration by resonance with a medium such as ink.

On the other hand, in the above embodiments, an example in which thesingle ink level detecting unit 10 is provided in the ink tank 11 hasbeen described. However, the plural ink level detecting units may set onthe inner wall surface of the ink tank 11 so that their height (depth)positions differ from each other, and the ink level may be measuredwhile the excitation pulse applied to each ink level detecting unit isswitched to the ink presence pulse or the ink absence pulse. Hereby, notonly the existence of the ink but also the ink level can be measured.

Further, in the above embodiments, the two kinds of excitation pulses;the ink presence excitation pulse and the ink absence excitation pulseare previously registered. However, assuming that ink which is differentin properties of matter, for example, viscosity is used, it is possibleto register previously plural kinds of excitation pulses.

Next, with reference to FIGS. 10 to 12, a fourth embodiment of theinvention will be described. The ink level detecting unit of theinvention can be provided for an ink cartridge attached to an ink jetprinter detachably, and this embodiment shows such the example.

FIG. 10 is an exterior perspective view of an ink cartridge 100 forwhich an ink level detecting unit in this embodiment is provided. Theink cartridge 100 has a housing 140 which houses one kind of ink as anarticle of consumption therein. At the lower portion of the housing 140,an ink supply port 110 for supplying ink to a printer described later isprovided. At the upper portion of the housing 140, there is provided alogic circuit 130 composed of a loop antenna 120 for communication withthe printer by radio waves and a special IC chip. At the side portion ofthe housing 140, a sensor SS used for measurement of the ink level isequipped. The sensor SS is electrically connected to the logic circuit130.

FIG. 11 is a sectional view of the sensor SS equipped for the sideportion of the housing 140 of the ink cartridge 100. The sensor SSincludes the above-mentioned piezoelectric element 12, two electrodes110, 111 which apply voltages to the piezoelectric element 12, and asensor attachment 112. The electrodes 110, 111 are connected to thelogic circuit 130. The sensor attachment 112 is a structure part of thesensor SS having a thin film which transmits vibration from thepiezoelectric element 12 to the ink and the housing 140.

FIG. 11A shows a case in which the predetermined quantity of ink andmore remains, and a liquid level of ink is higher than the position ofthe sensor SS (in FIG. 10). FIG. 11B shows a case in which thepredetermined quantity of ink and more does not remain, and the liquidlevel of ink is lower than the position of the sensor SS (in FIG. 10).As known from these figures, in case that the liquid level of ink ishigher than the position of the sensor SS, the sensor SS, the ink, andthe housing 140 function as vibration bodies. However, in case that theliquid level of ink is lower than the position of the sensor SS, thesensor, the housing 140, and only a small quantity of ink attaching tothe sensor SS function as vibration bodies. In result, vibrationcharacteristic around the piezoelectric element 12 changes according tothe residual quantity of ink. In this embodiment, also, using such thechange of vibration characteristic, the ink level is measured. Since thedetailed method of measuring the residual quantity is similar to thosein the first and second embodiments, its description is omitted.

FIG. 12 is a block diagram centered at the logic circuit 130 composed ofthe special IC chip provided for the ink cartridge 100. The logiccircuit 130, similarly to the cases in the first and second embodiments,includes an excitation pulse generating part 13 for applying anexcitation pulse to the piezoelectric element 12; a sensor 14 whichdetects a frequency of a counter electromotive force waveform based onresidual vibration by resonance with ink produced in this piezoelectricelement 12; a judgment part 15 which judges the existence of ink; and acontrol part 200 which controls theses excitation pulse generating part13, sensor 14, and judgment part 15. Further, in addition to theseparts, the logic circuit 130 includes a RF converter 202.

The RF converter 202 includes a demodulation part (not shown) whichdemodulates the radio waves received from a printer 302 through the loopantenna 120, and a modulation part (not shown) which modulates thesignal received from the control part 200 and sends the modulated signalto the printer 302. The printer 302 sends, using the loop antenna 120, abase band signal to the ink cartridge 100 with the carrier wave of thepredetermined frequency. On the other hand, the ink cartridge 100, byvarying a load of the loop antenna 120 without using the carrier wave,can vary impedance of the loop antenna 120. The ink cartridge 100, usingthe variation of this impedance, sends a signal to the printer 302.Thus, the ink cartridge 100 and the printer 302 can perform bilateralcommunication.

Further, the logic circuit 130, in addition, includes a power generatingpart (not shown) which rectifies the carrier wave received by the RFconverter 202 and generates electric power at the predetermined voltage(for example, at 5V). This power generating part supplies the electricpower to the RF converter 202 and the control part 200. Further, acharge pump circuit maybe provided, which raises the predeterminedvoltage generated by the power generating part to the predeterminedvoltage which the sensor SS requests and supplies the electric power tothe sensor 14.

As described above, in this embodiment, since not only the vibrationelement but also the excitation pulse generating part, the sensor, thejudgment part, the filter means, and the frequency detecting means areprovided for the ink cartridge, the ink cartridge itself can detect thefrequency of the counter electromotive force waveform from the vibrationelement based on residual vibration by resonance with the medium in theink cartridge, so that the existence of ink can be surely judged.

Further, without receiving influences by the individual difference ofeach ink cartridge, for example, even in case that the ink cartridge isexchanged, the exact detection can be performed.

Further, in the embodiment, between the ink cartridge 100 and theprinter 302 side, exchange of data is performed using radiocommunication. The printer body can stably exchange the data with theink cartridge 100 which moves together with a carriage in printingwithout fear of poor contact of a contact.

As described above, according to the invention, detects the residualvibration, which is produced by applying excitation to the vibrationelement such as the piezoelectric element, by resonance with the mediumsuch as the ink that comes into contact with the vibration element canbe surely detected without receiving the influence such as noise, sothat ink detection accuracy and reliability can be heightened.

Further, also in case that foaming and waving of the ink liquid levelare produced due to the movement of the carriage, the erroneousdetection can be prevented.

Further, by using the ink level calculating method by software together,the ink-end can be detected more exactly.

Further, the invention can be realized in various embodiments. Forexample, by the ink level detecting unit and detecting method describedin the above embodiments, an ink jet printer, an ink cartridge used inthe printer, a printer head, and also by a computer program forrealizing their methods or functions of the unit, and a recording mediumstoring its computer program, the invention can be realized.

Further, the invention can be similarly applied also to, as an ink jetrecording apparatus, a facsimile, a copying machine, and a plotter whichhave the similar ink jet system.

Industrial Applicability

The invention can be utilized in order to detect consumption state (inklevel) of ink in an ink container used in an ink jet recordingapparatus.

1. An ink level detecting unit including a vibration element providedfor an ink tank which houses ink, an excitation pulse generating partwhich applies an excitation pulse to this piezoelectric element, asensor which detects a frequency of a counter electromotive forcewaveform from the vibration element based on residual vibration byresonance with a medium in the ink tank, and a judgment part whichjudges the existence of ink on the basis of the frequency detected bythe sensor, wherein said sensor includes at least one filter means whichcauses only a waveform in the predetermined frequency band that has beenpreviously assumed according to the presence or absence of ink to pass,and a frequency detecting means which binarizes the counterelectromotive force waveform from the vibration element, counts thenumber of pulses of the binarized counter electromotive force waveform,counts time from the predetermined number-th pulse to the predeterminednumber of pulse, and detects the frequency of the counter electromotiveforce waveform on the basis of this time.
 2. The ink level detectingunit according to claim 1, wherein said filter means comprises a bandpass filter for ink presence, and a band pass filter for ink absence,which cause only the waveforms in the predetermined frequency bands thathave been previously assumed according to the ink presence and inkabsence respectively to pass; and said frequency detecting means detectsthe frequency of the counter electromotive force waveform that haspassed through said band pass filter for ink presence or band passfilter for ink absence.
 3. The ink level detecting unit according toclaim 2, wherein said frequency detecting means comprises a frequencycounter for ink presence which detects a frequency of the counterelectromotive force waveform that has passed through the band passfilter for ink presence, and a frequency counter for ink absence whichdetects a frequency of the counter electromotive force waveform that haspassed through said band pass filter for ink absence.
 4. The ink leveldetecting unit according to claim 2 or 3, wherein in said band passfilter for ink presence and said band pass filter for ink absence, eachcenter frequency is matched with a resonant frequency of said vibrationelement in a case of the ink presence or in a case of the ink absence;and each pass band is set at the size that can permit the individualvariation in said vibration element.
 5. The ink level detecting unitaccording to any one of claims 2 to 4, wherein an insensitive band isprovided between the pass bands of both band pass filter for inkpresence and band pass filter for ink absence.
 6. An ink jet recordingapparatus having the ink level detecting unit according to any one ofclaims 1 to
 5. 7. An ink cartridge, which houses ink used in printingand is detachably mounted on an ink jet recording apparatus, including avibration element provided for the ink cartridge, an excitation pulsegenerating part which applies an excitation pulse to this piezoelectricelement, a sensor which detects a frequency of a counter electromotiveforce waveform from the vibration element based on residual vibration byresonance with a medium in the ink cartridge, and a judgment part whichjudges the existence of ink on the basis of the frequency detected bythe sensor, wherein said sensor includes at least one filter means whichcauses only a waveform in the predetermined frequency band that has beenpreviously assumed according to the ink presence or ink absence to pass,and a frequency detecting means which binarizes the counterelectromotive force waveform from the vibration element, counts thenumber of pulses of the binarized counter electromotive force waveform,counts time from the predetermined number-th pulse to the predeterminednumber of pulse, and detects the frequency of the counter electromotiveforce waveform on the basis of this time.
 8. The ink cartridge accordingto claim 7, wherein said filter means comprises a band pass filter forink presence, and a band pass filter for ink absence, which cause onlythe waveforms in the predetermined frequency bands that have beenpreviously assumed according to the ink presence and ink absence topass; and said frequency detecting means detects the frequency of thecounter electromotive force waveform that has passed through said bandpass filter for ink presence or band pass filter for ink absence.
 9. Theink cartridge according to claim 8, wherein said frequency detectingmeans comprises a frequency counter for ink presence which detects afrequency of the counter electromotive force waveform that has passedthrough the band pass filter for ink presence, and a frequency counterfor ink absence which detects a frequency of the counter electromotiveforce waveform that has passed through said band pass filter for inkabsence.
 10. The ink cartridge according to claim 8 or 9, wherein insaid band pass filter for ink presence and said band pass filter for inkabsence, each center frequency is matched with a resonant frequency ofsaid vibration element in a case of the ink presence or in a case of theink absence; and each pass band is set at the size that can permit theindividual variation in said vibration element.
 11. The ink cartridgeaccording to any one of claims 8 to 10, wherein an insensitive band isprovided between the pass bands of both band pass filter for inkpresence and band pass filter for ink absence.
 12. The ink cartridgeaccording to any one of claims 8 to 11, further comprising an antennawhich sends and receives radio waves between an ink jet recordingapparatus and it, and a RF converter which demodulates the signalreceived from said ink jet recording apparatus through the antenna toinput the demodulated signal to a control part, and modulates the signalreceived from said control part to send the modulated signal to said inkjet recording apparatus through said antenna.
 13. The ink cartridgeaccording to any one of claims 8 to 12, wherein said excitation pulsegenerating part, sensor, judgment part, filter means, frequencydetecting means, and RF converter are provided, as a special IC chip,for the cartridge.
 14. A method of detecting level of ink in an ink tankused in an ink jet recording apparatus, comprising the steps of applyingan excitation pulse to a vibration element provided for the ink tank,detecting a frequency of a counter electromotive force waveform from thevibration element based on residual vibration due to resonance with amedium in the ink tank, and judging the existence of ink on the basis ofthe detected frequency, wherein Of the counter electromotive forcewaveforms from said vibration element, only the waveform in thepredetermined frequency band that has been previously assumed accordingto ink presence or ink absence is caused to pass by a filter means; thewaveform that has passed is binarized and the number of pulses of thebinarized waveform is counted; time from the predetermined number-thpulse to the predetermined number of pulse is counted; and a frequencyof said counter electromotive force waveform is detected on the basis ofthis time.
 15. The ink level detecting method according to claim 14,wherein a method of detecting the ink level by counting the number ofdots of ink ejected from a print head in the ink jet recording apparatusis used together.